This invention relates to a data storage system primarily for use as a digital video server in television broadcast and post-production facilities. In recent years, digital video servers have begun to revolutionize the television industry in much the same way as the introduction of the video tape recorder. Video servers have played a backstage role at many television facilities for years, first making their appearance to provide instant replay capabilities for broadcasts of sporting events.
A video server is essentially a high-speed data storage system with additional, dedicated hardware added. The additional hardware handles the functions of accepting signals in the North American Television Systems Committee (NTSC) format (consisting of a video signal and one or more associated audio signals) and sampling, quantizing and compressing the signals into a format suitable for digital storage. Other dedicated hardware decompresses the stored digital data and restores it to the original NTSC format signals.
Additional capability, often in software, may be provided to index, catalog and process the stored television signals. The extremely large amount of information contained in a television signal requires enormous amounts of magnetic disk storage to contain the digital representation of the video without visible distortion on playback. Substantial decreases in cost and advances in speed and performance of the disks and processing power required have made video servers increasingly popular in broadcast facilities. Advances in digital video compression have also reduced the cost and improved the quality of modern video servers.
One advantage of a video server is that, unlike a video tape recorder, a video server can record and play video simultaneously. If sufficient capability exists on the disk storage units and the internal data buses of the video server and enough compression and decompression hardware exists, multiple channels of video and audio can be recorded and played back at the same time. One example use of the video server is to start recording an interview with a winning athlete immediately at the conclusion of a sporting event while the broadcast station is transmitting a commercial message. When the commercial is completed, the broadcast station can then play the beginning of the recorded interview from the video server even though the video server is still recording the live interview. At the same time, journalists can be accessing the stored material, creating new video sequences by splicing the stored material with other stored material, and viewing the resulting new video sequence, transmitting it to other television facilities, or storing it to magnetic tape for later broadcast.
Although advances in computer, video compression, and magnetic storage have greatly reduced the cost and improved the recording quality of video servers, broadcast-quality video servers are still very expensive due to the fact that very high data rates are required to store high quality video without introducing visible distortion. This requires much faster hardware and larger disk capacities than that normally employed in computers designed for consumer-quality digital video. For example, many home computers can now easily play a single channel of MPEG-1 video at 1.5 to 3 million bits per second (Mbps). By comparison, a typical configuration of a broadcast video server will permit two channels of broadcast quality video, each channel requiring a record rate of around 20 Mbps, with no skips, pauses, or glitches.
When video servers are used in a networked environment to permit workstation access to the stored video for viewing and editing purposes, new problems arise. The common 10BaseT Ethernet networking standard permits a maximum data rate of 10 Mbps, insufficient for even a single channel of 20 Mbps video. The use of 100BaseT, with 100 Mbps capacity, theoretically increases this capability to 5 simultaneous channels maximum, although the actual capability is lower due to transport overhead, limiting the number of users who could simultaneously access stored material to 4.
The introduction of digital television (DTV) and in particular high definition television (HDTV), with data storage rates in excess of 45 Mbps, exacerbates the problem even further. However, even if the networking were not a problem, current video server designs will not support a large number of simultaneous accesses to the stored video content. One solution might be to duplicate the content across multiple video servers, but this would be extremely expensive and would still not be able to accommodate simultaneous requests from a large number of users on the network for a temporarily popular piece of content.
Yet another problem emerges with the requirement established by the U.S. Federal Communications Commission that television broadcast stations in the top U.S. markets be equipped to transmit digital television signals within a limited period of time. A typical television broadcast station represents the cumulative investment of millions of dollars and thousands of man-years of effort to create, transport, store, process and transmit a single, well known television format. The new regulations essentially require a new station to be built within the original in a fraction of the time that was taken to build the original station to perform the same functions with the new format. Television stations will need to accommodate the requirements of creating, storing and transmitting two different types of television signals. Initially, however, the new television signal will simply be the same content as the first, but in a converted format.
When stations first begin to transmit DTV, many stations will continue to create NTSC and simply convert NTSC to DTV just prior to broadcast, but as more and more content is created in DTV, stations will need to mix and manage the two types of content. Video servers will play an important role in helping television stations accomplish this task.
Although rapidly decreasing in price, the high cost of broadcast video servers restricts their use for direct to broadcast applications where time to air is critical and video tape recorders do not satisfy broadcast requirements. Video servers are highly effective for non linear editing applications, which allow specific points in a video clip to be accessed instantly, without having to quickly wind the tape through the intervening portions. However, the cost and bandwidth restrictions mentioned above put them out of reach of video journalists that might otherwise make use of the advanced editing capabilities.
The invention solves the problems of managing the storage of the same television content in multiple formats, creating and editing new clips composed of combinations of previously stored content in multiple formats simultaneously, and providing networked access to content stored on high-quality broadcast video servers by large numbers of users. The invention accomplishes this by storing incoming television signals consisting of video and associated audio in multiple different formats simultaneously. The different formats can be stored in a single data storage unit or in separate storage facilities.
Timing information is added to the different digital formats created so that synchronization between the stored formats can be established. This correlates a point in content recorded in one format with the same point in the corresponding clip recorded in another format. The timing information can then used by nonlinear editing software programs to duplicate editing changes made in one format to the same content stored in another format or formats.
Users on a networked system can browse and review content stored at a reduced bit rate using ordinary desktop computers. Utilizing editing software on the reduced resolution content, a user can create an edit decision list (EDL) with timing information embedded in the reduced-resolution format clip. The invention uses the synchronization information to apply the EDL to other stored formats of the same content without further user intervention. In this manner a user can create clips in multiple formats simultaneously by performing edits in a single, readily accessible format while the integrity of the high resolution format is maintained for broadcast purposes.